The present invention is directed to an improved chute corner design for a strapping machine (or “strapper”). More particularly, the present invention is directed to a chute corner assembly with a spring loaded chute liner.
Strapping machines are in widespread use for securing straps around loads. One type of known strapper includes a strapping head and drive mechanism mounted within a frame. Mounted to the frame is a chute through which strapping material is fed. Means generally are provided in the chute for guiding and retaining the strap in the chute so that the strap cannot fall or be pulled inwardly against the load until after the loop has been formed. Such means usually include a strap release system that permits the strap to be released from the chute upon tensioning.
Typically, the chute is larger than the load to be strapped so as to accommodate various load sizes and, thus, such strap guiding and retaining means function to initially maintain the strap in the largest possible loop configuration and, of course, function to permit the strap to be fed around the load without impinging upon or snagging upon the load. Moreover, the chute typically is constructed in a shape and size suitable to surround the load to be strapped, and generally is constructed in a quadrilateral shape, such as a square or a rectangle, with four corners, since most loads to be strapped share the same shape.
Prior art chute designs generally employ modular chute components, which are assembled to form the desired chute size and shape. For square and rectangular chutes, the chutes generally are comprised of horizontal and vertical chute sections, which often are supported by lightweight but sturdy aluminum support beams, and connected by four corner assemblies, typically constructed of a glass filled nylon material. The chute typically is enclosed by a strap retaining and release means of the type well known in the prior art.
Additionally, to facilitate the travel of the strap through the chute, many prior art chute designs also include chute liners mounted on the chute sections and within the chute. Such chute liners typically are slidably mounted or clipped on to the support beams, and are constructed to provide a smooth, flat surfaced along which the strap traverses during its travel around the chute. Preferably, the chute liner has a low coefficient of kinetic friction to facilitate movement of the strap through the chute. Additionally, such chute liners are machined to a precise length so as to minimize any gaps between the ends of the chute liners and the adjacent corner assemblies. For the reasons discussed below, the existence of such gaps adversely affects the travel of the strap through the chute.
In a typical stationary bottom-seal strapper, the chute is mounted at about a work surface, and the strapping head is mounted to a horizontal portion of the chute, below the work surface. The drive mechanism is also mounted below the work surface, near to the strapping head. The drive mechanism “pulls” or feeds strap material from a source, such as dispenser, into the machine. The drive mechanism urges or feeds the strap through the strapping head, into and around the chute, until the strap material returns to the strapping head to form a loop. After the strap loop has been formed, tension is applied to the strap to constrict the strap loop about the article and the overlapping strap ends are secured by conventional means.
Traditional side-seal strappers employ a similar configuration, except that the strapping head is mounted to a vertical portion of the chute, with the drive mechanism positioned in lateral proximity to the strapping head for the strap material. However, from an operational perspective, side-seal strappers and bottom-seal strappers are more or less equivalent.
Many such machines are employed in processes that maximize the use of fully automated operation. To this end, machines are configured for automated in-feed and out-feed, such that a load to be strapped is automatically fed into the machine by an in-feed conveyor, the strapping process is carried out, and the strapped load is automatically fed out of the machine by an out-feed conveyor. As such, an improper strapping event, such as a strap short feed, wherein the strap does not create a full loop around the load, can create a detrimental “ripple effect” along the entire automated strapping process by forcing the shutdown of an entire strapping line. Thus, it is critical to ensure that the occurrence of improper strapping events is minimized.
One of the major causes of improper strapping events is a strap short feed. A strap short feed occurs, as discussed above, when the strap does not create a full loop around the load. Strap short feeds are an inherent problem in prior art modular chute designs in which multiple chute sections and corners are assembled to form a desired chute size and shape. The interface between each chute section and each corner assembly creates potential areas where the strap may get impinged or snagged.
Specifically, frequent causes of strap short feeds in such prior chute designs are inherent gaps between the chute liners and the corner assemblies. Even a small gap can catch the leading edge of the strap material as it traverses through the chute causing the strap to hang or snag. The prior art has attempted to address the problem by altering the design of the chute liner.
For example, some chute liners are machined with a bevel on the leading edge of the chute liner. The bevel is intended to minimize the effect of any gap between the end of the chute liner and the adjacent face of the corner assembly. Similarly, the prior art has resorted to precise measurement and machining of the end of the chute liner so as to minimize the size of the gap.
However, such precise machining of the chute liner adds cost and time to the strapper manufacturing process. Moreover, since the chute liner often is comprised of a different material than the chute sections and corner assemblies, and since the different materials exhibit different thermal expansion and contraction rates during use, the precise machining of the chute liner often is of limited effect. A negligible gap between the chute liner and the corner assembly present during the manufacture of the strapper may expand into a troublesome gap under various operating conditions.
Accordingly, there is a need for an improved chute corner assembly designed to minimize the undesirable gap between the chute corner assembly and the chute liner. Desirably, such a chute corner assembly includes a recess for receiving the end of an adjacent chute liner. More desirably, such a corner assembly includes a chute liner spring plate for engaging the end of the chute liner. Most desirably, such a corner assembly includes a spring mechanism to bias the chute assembly away from the corner assembly and toward the opposite corner assembly in order to dynamically minimize any gap between the chute liner and the opposite corner assembly by allowing for spring-biased slidable movement of the chute liner between opposite corner assemblies during thermal expansion and contraction of the chute components.